Reenforced asbestos cement sheet



Oct. 24, 1933. HURDEN ETA 1,931,494

REENFORCED ASBESTOS CEMENT SHEET Filed NOV. 20, 1931 EVELYN HURDEN-ALFRED PERCIVAL HURDEN- STEPHEN EDWARD BEE5ON- INVENTORS:

ATTORNEYS:

Patented ct. 2 4,1933

mural) STATES PATENT OFFICE Hurden, Northwood,

and Stephen Edward Beeson, Rickmansworth, England Application November20, 1931, Serial No.

576,286, and in Great Britain December 5,

6 Claims.

The subject of this invention is a method of reenforcing asbestos cementgoods of the kind composed of .a mixture of Portland or other cementwith asbestos fibre made up of a number of thin layers-or laminationsinto sheets of the required thickness on a machine, as distinguishedfrom goods originally made up from material in plastic state, pouredinto shape or otherwise cast or moulded. These sheets made up oflaminated asbestos cement are then known as wall board if used in a flatcondition, but may be shaped or moulded while wet from the machine tovarious shapes, for example roofing tiles and corrugated sheets.

It is well known to insert wire or asbestos braid reeinforcements intosheets of material made by casting or pouring in one operation or byramming into a mould, and it has been proposed to insert expanded metalalready shaped to the re- 20 quired form into cast concrete material, toinsert fiat strips of metal into boards made of wood pulp beforeconsolidation, and to draw lengthsv of wire or woven wire webbing intoslab moulded in one thickness in a machine; but the present inventiondoes not relate to these matters, but to asbestos cement goods built upin layers as aforesaid.

Various attempts have been madeto reenforce asbestos cement materialswith ordinary wire, or 30 wire-netting,'chiefly by pressing between twowet sheets or by feeding the reenforcing material into the asbestoscement material while it is being .made on the machine, the reenforcingmaterial being inserted indiscriminately all over the sheet; but theresults have not been found satisfactory owing partly to the excessivecost, partly to the fact that adhesion between the laminations or sheetsis destroyed by the insertion of any continuous or substantiallycontinuous sheet of material for reenforcement, and partly, to the factthat the reenforcing material was not sufficiently flexible. It is alsofound thatany round or square wire of suflicient strength, or similarreenforcing material of more or less round or square section, cuts intothe asbestos cement material, thus weakening it and causing cracking. Ithas also been found impracticable to feed wire-netting on to the makingroll, as it is not sufiiciently flexible and destroys the film, and isalso liable to damage the machine, and furthermore is liable to causeseparation of the layers of sheeting According to the invention, areenforcement is incorporated in the material in the form of very 5:,thin and relatively narrow bands, ribbons or in which tensile strengthis requisite.

It is preferred to incorporate the reenforce ment in the sheets whilethey are being built up on the machine, because if it is insertedbetween two thin sheets of the asbestos material and the sheets pressedtogether, the effects of the pressure render it difficult to mould thesheets into any other than a fiat form.

The reenforcement must have the followin characteristics:-

It must have high tensile strength.

The strips must not be so wide as to separate the layers of asbestoscement for too great a distance and thus to interfere with the adhesionof the said layers to each other.

It must have extreme flexibility in a longitudinal direction so thatwhen fed on to the making roller of the machine it will not spring off;but lies in a curve corresponding with that of the making roller untilthe succeeding layer covers it; and it must also be flexible in atransverse direction so that when moulding, it does not distort or crackthe sheet.

It must not be thick enough to distort the surface of the asbestoscement sheet, or to cause a longitudinal crack in the asbestos cement inthe direction of its length, or to interfere with the building up of theasbestos cement sheet on the making roller.

It must not interfere with the subsequent moulding of the asbestoscement sheet into any shape required.

It must have suflicient adhesion to prevent it slipping when theasbestos sheet is placed under tension by a load in use.

' It must not be subject to corrosion or other deterioration in use.

A narrow band of textile material, such as flax tape, or a mixture ofhigh grade woven asbestos fibre with other textile fibre have been foundto meet these requirements most nearly. The strips may be made of wovenor plaited manilla, sisal, or any other fibrous material treated to makeit rot-proof and twisted, woven or plaited into the desired shape andtexture. 4

The strips may be notched, perforated, painted, or roughened in anyconvenient manner to ensure adhesion between them and the asbestoscement. The strips, or preferably the tapes are inserted in exactly thepositions where extra tensile strength is expected to be needed when-inuse, running in any direction or directions that may be consideredadvisable, and they may have projections in any direction to give extrastrength and prevent cracking of,the sheet; for instance, they may runlongitudinally or transversely of the sheet, or both longitudinally andtransversely, or diagonally or spirally, or other cross tapes may beused. They may be inserted at the edges of a semi-circular ridge, oradjacent to the upward bends of a ribbed tile, or at the bottom bands ofa corrugated sheet, or at both the bottom and top of each corrugation,although they are more useful in the troughs or corrugations to resisttension than at the tops or crests of corrugations.

The reenforcement is to be used purely as a tensile reenforcement, thatis, to resist tension under load, and is not intended as a beam orsupport to the tile or sheet, the latter itself being sufiicientlystrong in compression. The tensile reenforcement bands assume theircorrect position in the finished moulded article, that is, the flexiblereenforcement is placed in a position to give maximum resistance totension when the sheet is moulded into a series of corrugations or risesand depressions. The top portion of each corrugation or rise takes thecompression load, and the bottom of the corrugation or channel takes thetensile strain, when a load is applied to the corrugated As the materialis strong in compression and relatively weak in tension, tensilereenforcement is necessary to balance the resistance and get maximumstrength. The neutral axis lies approximately on a line taken throughthe centre of the corrugations. A fiat sheet without mouldings orcorrugations would not be reenforced to anything near the same extent asa corrugated one, as the reenforcement would be on the neutral axis. Themain reenforcement is therefore placed in a position to take up thegreatest tensile strain, although it may be advantageous to combine withthis main reenforcement subsidiary cross reenforcements of much lessstrength to tie the sheet together and resist shear under load.

In order that the said invention may be clearly understood and readilycarried into effect, the same will now be described more fully withreference to the accompanying drawing illustrating some exemplificationsof the invention.

Figure 1 illustrates the application of the reenforcement to a wallingsheet.

Figure 2 represents the edge of a corrugated sheet reenforced in thesloping parts.

Figure 3 represents the edge of a-cprrugated sheet reenforced at thetops and bottoms of the corrugations.

Figure 4 is a perspective View of a corrugated tile embodying theinvention.

Figure 5 is a perspective view of the corner of a flat sheet embodyingthe invention. a,

Figure 6 is a diagrammatic elevation of apparatus in which thereenforcement is introduced in the manufacture of a sheet of asbestoscement.

In all the figures, A indicates generally the basic material used and Bthe reenforcing strips or tapes, which in all cases must be narrow andthin relatively to the dimensions of the sheet of the basic material,and spaced sufliciently wide apart to leave portions of the sheetbetween each strip of much greater area than the area occupied by theadjacent strips. In the examples according to Figures 4 and 5 thereenforcement takes the form of a very wide-meshed netting, andwire-netting would of course not be suitable.

The reenforcing strips or tapes may be placed in any position betweentwo wet sheets of ashes-- tos cement each constituted of a number ofthin laminations and each of approximately half the requisite totalthickness, before setting and pressing the sheets together, but they arepreferably fed into the asbestos cement while it is being made up on themaking roller, the strips being inserted when about half the requisitenumber of thin layers of the material have been built up, and theremaining layers being built up over the reenforcing strips; I sertedduring manufacture without loss of time or stoppage of the machine.method of inserting the strips is illustrated in Figure 6, in which Cindicates the making roller, D the felt roller or pressing roller, and Ethe travelling blanket of felt on which a film a of asbestos cement isbrought to the making roller to be wound thereon. The reenforcing stripsor tapes can. be laid over the film to be carried on to the makingroller, or can be fed from a separate roller and reach the surface ofthe film a at an angle as seen in the drawing. Many forms of mechanismcould be used to carry out these operations, and it is not considerednecessary to illustrate more particularly any examples of suchmechanism,- which does not constitute any part ,of this invention. sheetor other article between spaced supports They can thus be in- Thispreferred 85 In cases where a corrugated or otherwise moulded sheet ortile rests on intermediate supports and is uniformly loaded, the partsbetween the supports are subject to tensile stress at the bottom of thesheet or tile,but at'the parts thereof over the intermediate supports,tensile stress also exists at the top of the sheet or tile, so that insome cases it is desirable to reenforce itboth at the top and bottom, asrespresented in Figure 3. In other cases, as in that of the tilerepresented in Figure 4, the channels between the corrugations areprovided with. fairly closely spaced reenforcing strips, and continuousor other cross strips of wider spacing, which may also be of lessstrength individually, follow the curves of the corrugations. 5

What we claim and desire to secure by Letters Patent of the UnitedStates is:-

1. A sheet of asbestos cement material reenforced with a plurality offlat ribbons spaced apart and made of extremely flexible material of 12high tensile strength, such as flax tape, which ribbons are very thinand narrow relatively to the width of the sheet, and solely located inand restricted to those parts of the sheet which are intended to besubjected to tensile stress when in use.

2. A sheet of asbestos cement material consisting of a number of thinlaminations of said material, between which laminations are enclosed aplurality of flat ribbons spaced apart and made of extremely flexiblematerial of high tensile strength, such as flax tape, which ribbons arevery thin and narrow relatively to the width of the sheet, and solelylocated in and restricted to those parts of the sheet which are intendedto be subjected to tensile stress when in use.

3. A sheet of asbestos cement material consisting of a number of thinlaminations of said material, between which laminations are enclosed aplurality of flat ribbons spaced apart and made of extremely flexiblematerial of high tensile strength, such as flax tape, which ribbonscross each other approximately at right angles and are individually verythin and narrow relatively to the width of the sheet, and solely locatedin and restricted to those parts of the sheet which are intended to besubjected to tensile stress when in use.

4. A corrugated sheet of asbestos cement material consisting of a numberof thin laminations .of said material between which laminations areenclosed a plurality of ribbons spaced apart and made of extremelyfiexible material of high tensile strength such as flax tape toreenforce the bottoms of the corrugations, which ribbons are very thinand narrow relatively to the width of the sheet.

5. A corrugated sheet of asbestos cement material consisting of a numberof thin laminations of said material between which laminations areenclosed a plurality of ribbons spaced apart and made of extremelyflexible material of high tensile strength such as flax tape toreenforce the tops and bottoms of the corrugations, which ribbons arevery thin and narrow relatively to the width of the sheet.

6. A corrugated sheet of asbestos cement material consisting of a numberof thin laminations of said material between which laminations areenclosed a plurality of ribbons spaced apart v and made of extremelyflexible material of high

